German Published Patent Application 3,042,246 and the corresponding U.S. Pat. No. 4,440,136 disclose a fuel metering system in which, for the purpose of acceleration enrichment, an enrichment factor is formed in accordance with a certain formula and the individual components of the formula can be called from memories as a function of load and rotational speed. The enrichment factor is given by FM=1+FM 1.times.FM 2. In this equation, FM 1 is rotational speed- and load-dependent and FM 2 is temperature-dependent.
German Published Patent Application 3,623,041 and the corresponding U.S. patent application Ser. No. 165,274, now U.S. Pat. No. 4,893,602 disclose a method for fuel metering in the case of acceleration, which takes account of the temporal relation between the occurrence of the acceleration demand signal and the intake valve times in order to allow the required additional quantity of fuel for implementing the acceleration demand to be metered-in in the best possible way with respect to time. For this purpose, provision is made inter alia, to divide the calculated additional quantity of fuel between a plurality of successive metering processes or to provide so-called interim injections.
The physical problem in acceleration enrichment is to make available the required additional quantity in the combustion chambers of the internal combustion engine themselves. This proves difficult, particularly at low temperatures, because part of the quantity of fuel metered into the induction pipe condenses on the walls of the induction pipe and is thus, in the final analysis, not immediately available for the actual combustion process. The fuel precipitating on the inside wall of the induction pipe forms a so-called wall film of fuel. It is dependent not only on the structural conditions but also, in particular, on the temperature, rotational speed, and load.
Since it is very difficult to control the build-up and dissipation of the wall film of fuel in the case of unsteady operating states of the internal combustion engine, various attempts to describe the wall film have already been published in the literature. A fundamental work on this subject can be found in SAE Paper 810494 "Transient A/F Control Characteristics of the 5 Liter Central Fuel Injection Engine" by C. F. Aquino.
It is the object of the present invention to provide an electronic control system for fuel metering in an internal combustion engine, in which an optimum transitional behavior with respect to the exhaust gas is achieved in the case of acceleration and deceleration processes.